The present invention relates to a coating process composed of an optically effective layer system, for CRT glass substrate, whereby the layer system has a high anti-reflection and low resistivity effect. More specifically the invention relates to a combination of vacuum sputtering process which produce high conductivity of oxide films and a wet process which produce silica overcoat from traditional spin coating.
U.S. Pat. No. 4,921,760,whose disclosure is an multi-layer anti-reflection coating with excellent adhesion between CeO2 layer and synthetic resin. The layer system including CeO2, Al2O3, ZrO2, SiO2, TiO2 and Ta2O5. All the thin films of the layer system are produce by vacuum evaporation or sputtering process. There are 3 to 5 thin layers in the layer system. For a given example, the total thickness of the 5 layer structure was about 3580 angstroms. The materials and thickness of the two most thicker films of the 5 layer structure are CeO2, 1360 angstroms and SiO2, 1220 angstroms respectively.
U.S. Pat. No. 5,105,310, whose disclosure is an multi-layer anti-reflection coating designed for deposition in in-line coating maching by reactive sputtering. The layer system including TiO2, SiO2, ZnO, ZrO2 and Ta2O5. All the thin films of the layer system are produced from vacuum evaporation or sputtering process. There are 4 to 6 thin layers in the layer system. For a given example, the total thickness of the 6 layer structure was about 4700 Angstroms. The materials and thickness of two most thicker film of the layer system are ZnO, 1370 Angstroms and SiO2, 1360 Angstroms respectively.
U.S. Pat. No. 5,091,244 and 5,407,733, disclosed a new type electric conductive light-attenuating anti-reflection coating. The major claim is an article comprision of nitrides of certain transition metal to provided an electrically-conductive, light-attenuating, anti-reflection surfaces. The layer systems including TiN, NbN, SnO2, SiO2, Al2O3, and Nb2O5. The thin films of the layer system are nitride and oxide materials. There are 3 to 4 thin layers in the layer system. For a given example, the total thickness of the 4 layer structure was about 1610 Angstroms. The materials and thickness of the two most thicker films of the layer system are ZnO, 650 Angstroms and SiO2, 820 Angstroms, respectively. The transmission of visible light of these two layer systems is below 50%. All the thin films of the layer system are produced by vacuum evaporation or sputtering process.
U.S. Pat. No. 5,147,125, whose disclosure is a multi-layer, anti-reflection coating using zinc oxide to provide UV rejection for wave-lengths shorter than 380 nm. The layer system including TiO2, SiO2, ZnO, and MgF2. All the thin films of the layer system are produced from vacuum evaporation or sputtering process. There are 4 to 6 thin layers in the layer system. For a given example, the total thickness of the 5 layer structure was about. 7350 Angstroms. The materials and thickness of the two major films of the layer system are Zno, 4390 Angstroms and MgF2, 1320 Angstroms, respectively. All the thin films of the layer system are produced by vacuum evaporation or sputtering process.
U.S. Pat. No. 5,170,291 disclose a 4 layer system which is optical effective and has a high anti-reflective effect. The layers can be formed by either a pyrolytic method, a plasma-supported chemical vapor deposition met hod, a sputtering method or a chemical deposition method. The layer system including SiO2, TiO2, Al2O3, Zns, Mgo and Bi2O3. For a given sample, the total thickness of the 4 layer structure was about 2480 Angstroms. The materials and thickness of the two major films of the layer system are TiO2, 1040 Angstroms and SiO2, 940 Angstroms, Respectively.
U.S. Pat. No. 5,216,542 whose disclosure is a 5 layer coating with high anti-reflection effect. The process use an adhesive layer of Ni, Cr or NiCr metal with a thickness about 1 nm (manometer). Other four layers are compose of SnO2, ZrO2, ZnO, Ta2O5, NiO, CrO2, TiO2, Sb2O3, In2O3, Al2O3, SiO2, TiN and ZrN. For a given example, the total thickness of the 5 layer structure was about 2337 angstroms. The materials and thickness of the two majority films of the layer system are TiO2, 500 Angstroms and SiO2, 1387 Angstroms, respectively. The transmission of visible light of this layer system is below 30%. All the thin films of the layer system are produced by vacuum evaporation or sputtering process.
U.S. Pat. No. 5,541,770 whose disclosure is a light attenuating anti-reflection coating including electrically conductive layers. It is a four or five layer system. A light absorption high refractive index metal such as Cr, Mo and W was used as a optically effective thin film in the layer system. The other three or four layers are TiO2, ITO, Al2O3, SiO2 and TiN. The patent shows that the majority materials of the layer system are oxide and nitride, only one metal film was used as an optical effective thin film in the anti-reflection coating. All the thin films of the layer system are produced by vacuum evaporation or sputtering process. For a given example, the total thickness of the 5 layer structure was about 1495 angstroms. The materials and thickness of the majority films of the layer system are ITO, 334 Angstroms and SiO2, 720 Angstroms. The transmission of visible light of this layer system is below 60%.
U.S. Pat. No. 5,362,552 whose disclosure is a 6-layer anti-reflection coating includes three layers of electrically-conductive metal oxide. The layer system including SiO2, ITO, Nb2O5, and Ta2O5. Up to a total optical thickness of about one-wavelength of visible light of the electrically conductive metal oxide may be included in the coating. For one of given example of 6 layer structure, the materials and thickness of the majority two layers within this 6 layer system are SiO2, 854 Angstroms and ITO 1975 Angstroms. All the thin films of the layer system are produced by vacuum evaporation or sputtering process.
U.S. Pat. No. 5,579,162 whose disclose is a 4-layer anti-reflection coating for a temperature sensitive substrate such as plastic. One layer is a DC reactively sputtered metal oxide which may be deposited quickly and without imparting a large amount of heat to the substrate. The layer system including SnO2, SiO2 and ITO. For one of given example of the 4 layer structure, the materials and thickness of the majority two layers within this system are SnO2, 763 Angstroms and SiO2 940 Angstroms. All the thin films of the layer system are produced by vacuum evaporation or sputtering process.
U.S. Pat. Nos. 5,728,456 and 5,783,049, disclosed an improved way to deposit anti-reflection coating on plastic film. The multi-layer thin films was coated by a roller coating with vacuum sputtering process. The layer system including ITO, SiO2, and a thin lubricating over layer which is a solvent-soluble fluoropolymer. For a given example, the total thickness of the 6 layer system was about 2630 Angstrom. The materials and thickness of the two major film of the layer system are Ito, 888 Angstrom and SiO2, 869 Angstrom.
The above description show clearly that all the films of a layer system with high anti-reflection effect was produced by vacuum evaporation and/or sputtering process. On the other hand, the thickness of the major layer of high refractive index materials in the layer system was between about 700 to 2000 angstrom and the thickness of the major layer of low refractive index materials in the layer system was between about 700 to 1400 angstrom.
An object of the present invention is to provide an anti-static coating by sputtering process combined with an anti-reflection coating by wet process.
The process of manufacturing transparent conductive oxide thin film in volume production was high reliable and was routinely need in the industries such as semiconductor, display, architecture glass and plastic web coating for a long time. Because of the low resistance and high transparent conductive oxide thin film was easy to deposit by sputtering process than wet process (either in process of spin coating or spray coating). The present invention provided the anti-static and anti-reflection coating in a combination system of vacuum sputtering and wet coating process. It is well known that the coating of conductive oxide materials such as SnO2, ZnO, In2O3, SnO2:F, SnO2:Sb, In2O3:Sn, ZnO:Al, Cd2SnO4, In2O3xe2x80x94ZnO, SnO2xe2x80x94ZnO and In2O3xe2x80x94MgO, etc. is quite high cost, low performance (high resistance), and low utilization (about 3xcx9c5% of chemical solution) from wet coating process. A roughly estimate show that for a conventional wet coating system of CRT surface of a total thickness of about 200 nm (ITO: 100 nm, silica: 100 nm) was required to form an anti-static effective (103xcx9c105 xcexa9/square) and optically effective anti-reflection coating. Experimentally shows that wet coating process of conductive oxide materials such as ITO, ATO, IZO and AZO, etc. with a thickness above 100 nm impart low uniformity, high resistance, low transmittance and high cost due to the spin coating and dry baking from solution of those materials. For a typical conductive oxide sputtering process, the thickness of the thin film is below 50 nm to reach the resistance of 102xcx9c103 xcexa9/square, and the uniformity of the thin film is less than 3% which is important for optically effective in anti-reflection coating. On the other hand, for a wet process system the hardness of coating is about 6 H and for a vacuum sputtering process, the hardness of coating is about 9 H. The combination of vacuum sputtering process and wet process produce a coating with the hardness of about 8-9 H. The present invention is to provide the anti-reflection with anti-static layer system compose of basically three layers of oxide materials deposit by PVD system and only one layer of silica deposit by wet process from chemical solution. The design of vacuum sputtering process not only provide a high conductive ITO film in the CRT coating but also provide two layer of diffusion barrier to prevent the interaction between ITO and wet chemical. The present invention provided a high conductive anti-static process of anti-reflection coating which can be applied on the CRT surface coating.
There are four layer, namely, the first, second, third and fourth layers in consecutive numerical order beginning with the layer nearest from the substrate for the present invention of anti-reflection coating. The each layer was described in terms of physical thickness or optical thickness. The optical thickness is a mathematical product of a layers thickness and its refractive index. It is described as a fraction of a designed wavelength. In the present invention the designed wavelength is about 520 nm.
The first or the innermost layer 1 is a transparent conductive oxide material. The conductive oxide layer, preferably ITO, substantially little absorption for visible light, has a refractive index between 1.85 to 2.1 at a wavelength of about 520 nanometer (nm) and an optical thickness of about one sixth to one tenth wave length at the design wavelength.
The second layer is an oxide material. The oxide layer, preferably SiO2, substantially non-absorption for visible light, has a refractive index between 1.45 to 1.50 at a wavelength of about 520 nanometer (nm) and a physical thickness of between 10 nm ato 50 nm at the design wavelength.
The third layer is also an oxide material. The oxide layer is similar to ITO in refractive index, preferably SnO2, substantially non-absorption for visible light, has a refractive index between 1.85 to 2.2 at a wavelength of about 520 nm and a physical thickness of about 40.0 nm to 60.0 nm at the design wavelength. The fourth layer is the same as the second layer, but the second layer material is coated by sputtering method and the fourth layer is prepared by wet process from TEIS solution. The material commonly is called silica. This layer has a refractive index between 1.45 to 1.55 and an optical thickness of about one fourth wave length at the design wavelength.
In the preferred embodiment, the four layers coating includes a first layer of ITO having a thickness of 40 nm in sample 1 and 25 nm in sample 2. A second layer of SiO2 having a thickness of about 20 nm in sample 1 and 25 nm in sample 2. A third layer of SnO2 having a thickness of about 40 nm in sample 1 and 55 nm in sample 2 and a fourth layer is a layer of silica having a thickness about 85 nm in both of sample 1 and sample 2.
The stated objects are achieved by the invention, a low resistance between 102 xcexa9/squarexcx9c103 xcexa9/square can be obtain from the ITO coating, and a low reflection spectrum can be obtain on the CRT substrate in the visible range from 400 nm to 700 nm. All the reflection is below 5% at any wavelength from 400 nm to 700 nm in this 4 layers optical coating. It is demonstrated that the process is simple, reliable, easy control and economically. It has become possible in this way to produce an extremely low resistance, high hardness and low reflectance anti-reflection coating. Of particulate advantage, a batch or in-line sputtering system was suggest to deposit the first, second, and third layer of the present invention for low resistance, high optical performance and high scratch resistance. A wet coating process system was suggested to deposit the fourth layer of silica for low cost manufacturing.
On the other hand, the layer system of this invention is of high conductive for EMI (Electromagnetic Interference) shielding, extremely low reflection for optical view, high scratch resistance for surface hardness and low cost for manufacturing. For instance, a four layer anti-reflection and anti-static coating on CRT glass substrate according to the combination process of sputtering and wet process is described in this embodiment. The layer system has a low resistance between 102 xcexa9/square to 103 xcexa9/square to pass the certification of TCO 99, the layer system is hard enough to pass the scratch test of military standard MIL-C-48497 or MIL-C-675 and the optical quality is good enough to achieve the low reflection of CRT surface.
Thereby, a DC, AC or RF magnetron sputtering can be provide to deposit the first, second and third layer from ITO, Si and Sn targets in the presence of a sputter gas of mixture Ar and O2, under a given pressure of approximately 3 m Torr (m=mili=0.001). For the fourth layer, it is proposed that by using wet process method such as spin coating or spray coating from a TEIS solution in the presence of coating under a temperature of 33xc2x0 C. and baking condition of 200xc2x0 C./30 min.
In the sample 2, the thickness of first, second and third oxide layer is 25, 30 and 55 nm, respectively. The thickness of fourth layer of silica is 95 nm. In this case, the resistance is about 3.8xc3x97102 xcexa9/square and the optically performance is a lower reflection wide band coating. The photopic reflectance is lower than 0.5%. Accordingly, the present invention having a layer system composed of three sputtering layers and one wet coating layer which is a high performance and economic process for the anti-reflection with anti-static coating on CRT glass.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawing, in which: